What is the general formula for alkenes?

The general formula for alkenes is indeed CnH2n. Alkenes are hydrocarbons featuring at least one carbon-carbon double bond (C=C). The formula reflects that for every n carbon atoms, there are 2n hydrogen atoms. This relationship arises because the double bond reduces the number of hydrogen atoms that can be present compared to alkanes, which have the general formula CnH2n+2.

Thus, for each additional carbon in an alkene, a corresponding decrease of two hydrogen atoms occurs due to the presence of the double bond, leading to the alkene formula being specifically CnH2n. This formula applies to straight-chain alkenes and provides a clear way to determine the molecular formula of simple alkenes based on the number of carbon atoms they contain.